Conventionally, a combination of an ethylene-vinyl acetate copolymer resin (EVA) and a cross-linking agent represented by an organic peroxide has been frequently used as a sealing material sheet for a solar cell module. Further, in recent years, a sealing material sheet using a polyethylene-based resin has also become widely used instead of the EVA by taking advantage of the excellent water vapor barrier properties.
As a polyethylene-based sealing material sheet, for example, it has been also known from a sealing material by a modified ethylenic resin containing alkoxysilane as a copolymerization component. Furthermore, it has been known of a sealing material sheet in which such a modified ethylenic resin is mixed with a cross-linking agent, and the mixture is cross-linked by a modularization step or the subsequent heating step (see Patent Document 1).
On the other hand, in addition to a thermal cross-linking treatment method in which an organic peroxide is heated, a technique for improving the heat resistance of a sealing material sheet by performing a cross-linking treatment by irradiation with ionizing radiation onto the polyethylene-based resin and the like, without the use of a cross-linking agent has been disclosed as a method of cross-linking treatment (see Patent Document 2). Furthermore, a technique for imparting heat resistance by performing a cross-linking treatment by irradiation with ionizing radiation onto the linear low density polyethylene having a predetermined density or less, and by eliminating a heat curing step for a long time also without the use of a cross-linking agent has been disclosed (see Patent Document 3).
[Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2009-10277
[Patent Document 2] Japanese Unexamined Patent Application, Publication No. 2009-249556
[Patent Document 3] Japanese Unexamined Patent Application, Publication No. 2011-77357